We studied the role of several neuropeptides (angiotensin II, atrial natriuretic factor, substance P) and biogenic amines (dopamine, norepinephrine, serotonin) in the central regulation of the functions of the autonomic nervous system and the pituitary gland. Special emphasis was given to central cardiovascular control and the central control of fluid metabolism. The metabolism of biogenic amines in individual brain nuclei was studied by radioenzymatic assays and by high pressure liquid chromatography. Neuropeptide content of brain nuclei was studied by radioimmunoassays. Neuropeptide and biogenic amine receptors were studied in individual brain nuclei by quantitative autoradiographic methods with computerized microdensitometry and comparison to 125I-standards. Animal models included the spontaneously (genetic) hypertensive rat (SHR), the Brattleboro rat, unable to synthesize vasopressin, neurogenically hypertensive rats (sinoaortic denervated), acutely dehydrated rats and adrenolectomized, adrenodemedulectomized and hypophysectomized rats. We demonstrated a central role for angiotensin II and atrial natriuretic factor in genetic hypertension and dehydration, and a role for the biogenic amines, dopamine, norepinephrine, and serotonin in genetic hypertension and in the regulation of circadian rhythms.